Process for the gasification of dust or fine-grained fuels with circulating gas



April 12, v1938. H. SCHMALFELDT 2,113,774

PROCESS FOR THE GASIFICATION QFDUST OR FINE GRAINED FUELS WITH CIRCULATING GAS Filed Nov. 7, 1955 2 Sheets-Sheet 1 1 llll lllll Hans schmlgelaq INVENT E Fig-1. l 0 A'r'r y,

PROCESS FOR THE GASIFICATION OF DUST OR-FINE' GRAINED FUELS WITH CIRCULATING GAS Filed NOV. 7, 1935 2 Sheets-Sheet 2 April 1938- H. SCHMALFELDT 13,774

INVENTQE.

Patented Apr. 12, 1938 I v PROCESS FOR THE GASIFICATION OF DUST R FlNE-GRAINED FUELS WITH CIRCU- LATING GAS Hans Sohmalfeldt, Kassel, Germany Application November '1, 1935, Serial No. 48,730 In Germany November 26, 1934 4 Claims. (Cl. 48-202) In gasifying fuels for the purpose of producing During the gasification of dust fuels the fola gas free from nitrogen or poor in nitrogen, for lowing fundamental difilculties arise: example Water gas, even today large coke is The separation-of non-gasified and gasified coal chiefly employed. The use of coke presents the cannot be carried out in the gasifier owing to the 5 advantage that, during the hot blowing, a quanfact, that the gas-fuel dust mixture comprises 5 tity of heat can be accumulated in the glowing very slightly-gasified dust particles together with coke bed sufiicient to supply the quantity of heat almost completely gasified fuel dust particles all necessary for the gasification with water vapour of which are discharged from the gasifier together corresponding to the two equations with the circulating gas current. For this reason it is very difiicult to attain a complete gasificatlon 10 Q+ of the coal dust. The gasiflcation requires with C+ZHZO=CO2+ZEZ increasing degree of gasification very materially longer periods of treatment and consequently Under certain conditions, and particularly in the large gasifying chambers.

treatment of lignite and similar fuels which on Another difliculty, which, however, canbe more 15 account of their less firm structure are not suiteasily overcome by employing corresponding exable for the accumulation of the reaction heat, pense in apparatus is that "the circulating gas it may be preferable to carry out the gasification must be again freed from ash and fuel dust before w t the C08 in a fi rained or dust state. it is re-heated, on the one hand in order to're- The coal is preferably employed in a pulverous move the dust separated by reaction, but chiefly state, somewhat like lignite dust, in order to to prevent that part of the gasifylng plant which obtain the largest possible'surface. It has been effects the heating of the circulating gas from found that in the use of dust coal at very rapid becoming dusty. For re-heating the circulating gasification can be obtained with simultaneous gases either recuperators or regenerators may be treatment of a large quantity of coal dust. employed. The recuperators which are less often. 25

The quantity of heat required for the gasificaused will soon lose in efiiciency by becoming dusty tion may be introduced, by internal heating either and slaggy, if the circulating gases are not suitwith a gas which has a high oxygen content or ably cleansed before entering the recuperator. It with heated circulating gas. As the first method is similar in the case of regenerators which, if used possesses the disadvantage of the high expense of with non-purified circulating gas, not only be- 30 oxygen and the large content of carbon monoxide come dusty and slagged, but are also soon deand carbon dioxide in the gas produced, only the stroyed by slag flux. production of the reaction heat with highly heat- Besides the apparatus necessary for the gasifi ed circulating gas, consisting of water vapour or cation there is also the auxiliary apparatus for of a mixture of water vapour andgas produced in the drying and grinding of the coal to be gasified. 5 the process, comes into question when the gas It has been found, that for drying and grinding, produced is to have the smallest possible percenas a fine-grained or pulverous coal has to be gasitage of carbon dioxide and carbon monoxide and fied, circulating driers can advantageously be a large amount of hydrogen. fitted with combined material disintegration.

For gasifying fine-grained and pulverous fuels These driers work with a current of hot flue gases 40 by means of circulating gas a number of measures produced by a separate furnace, these gases floware necessary. First, the coal must be dried and ing through a riser or downcomer conduit. The ground to dust fineness. The dust coal must then previously broken coal is introduced into this be charged into the gasifier proper and gasified rapidly flowing flue gas current. A very rapid in the same, the highly heated circulating gases drying of the coal takes place owing to the direct 46 supplying the reaction heat. On leaving the contact with the rapidly flowing highly heated gasifier the residue coal, which has not been gasiflue gases and also by the continual disintegrafied, must be separated, together with the ash, tion of the coal particles due to the friction and. from the circulating gas cooled to a certain temimpact on the one hand and to surface drying and 50 perature. Then the circulating gas is again heat tension which is the difference in tempera '50 heated to a high temperature after the freshly ture between the surface of the fuel particles generated gas quantities have been separated and and their interior. The particles come from the again comes in contact with fresh dust coal for bunker in a cool state and are readily heated by further reaction. The whole process takes place the hot gases on their surfaces, while the in- 5 continuously. terior is stillcool. "Ihesufliciently fine, that is for disintegrating.

preferably dust-fine dry coal particles are separated by wind separation, whereas the coarser and not yet sufficiently dry particles pass along the drying path in being again passed through a coarser or finer disintegrating apparatus, until fineness and degree of dryness are sufficient. The dust coal or fine coal is separated from the exit gases generally by several dust removing devices arranged one behind the other and the flue gases freed from dust, and cooled are discharged into' the atmosphere. The dust separation evidently also requires particular care during the circulating drying. Usually an electric dust purification is arranged in series with one or several centrifugal separators, so that there are often three or more dust removing plants connected in series.

In the production of water gas from a layer of finely divided fuel by means of air and steam it has already been proposed to use the gases escaping from the production of gas for dryin the fuel, the process working in direct current.

According to the invention a considerable improvement and also simplification can be obtained in the gasification of dust coals with circulating gas by simultaneously employing the latter as a circulating dryer for the production-of the dry dust coal in the procedure hereinafter set forth:

The finely divided carbonaceous fuel (mineral coal, charcoal, lignite, peat, etc.) is gasified in a gasifying zone by means of circulating gas of about 700-1600 C. The circulating gasalways contains steam, together with e. g. water gas of different composition or hydrogen and carbonic acid or producer gas. The gases, escaping from this zone and charged with the more or less gasified fuel dust, are used to dry the necessary amount of fuel, e. g. by means of drying appa- .idvan ratus (drying by means of a drum). tageously the raw fuel is introduced into the flowing gas stream; by the quick drying obtained thereby, the fuel is simultaneously disintegrated. This may be supplemented by mechanical means Thereupon the mixture of as and fuel is separated by suitable means and at this point a part of the produced ash and fuel diist (about 10-50% of the total amount produced by drying and. disintegrating) is removed from the circulation. The other part is led back to the gasifying zone. The gas is led-if necessary after washing and freeing it from the last ash and fuel dust particles-to the gasifying zone. In this way a part of the produced. gas is removed as final product; the amount of this final product naturally corresponds to the amount of gas produced during the circulation. Before the other part of the gas discharges into the gasifying zone, it is reheated. The fuel removed from the circulation may be used for this purpose. It may also be used to heat an air-heater which preheats the combustion air for the regenerators.

Advantageously the ash and fuel dust to be .removed from the circulation is taken from the dust separator which shows the highest content of ash.

From the foregoing it is clear that according to the present invention it is possible to combine the asifying known per se with a special method of drying byintroducing the raw fuelinto the gas stream escaping from the gasifying zone, whereby also disintegrating of the lumps of raw fuel takes place. This method is followed by removing a part of the so produced dust of fuel, advantageously afterseparation from the gas and before intrdduction into the gasifying zone. In-

lating gas.

stead of the first described method of simultaneously drying and disintegrating also an ordinary drying of the raw fuel by means of the gases escaping from the gasifying zone may take place combined with mechanical means for disintegrating the raw fuel.

Two forms of embodiment of an apparatus suitable for carrying out the process as above described are illustrated in diagrammatic form in the accompanying drawings in which Fig. 1 illustrates one form of apparatus and Fig. 2 another form.

Referring now to Fig. 1 the fuel dust to be gasified is introduced into the gasifier a and b. Instead of one gasifier also' several gasifiers'may be used, being connected in series. The dust to be gasified is in suspension in the gasifier; The amount of the fuel in the gasifier is such that the suspension may be obtained and that the temperature necessary for the gasification may be maintained. The hot circulating gas enters at 0, whereas the more or less gasified fuel dust is discharged at d, together with the cooled circu- The circulating gases are-not cooled by a special measure, but this is effected thereby, that a part of their heat content is given ofi to the dust particles in the gasifier. These quantities of circulating gas charged with the more or less gasified dust particles are then used for drying and disintegrating the fresh coal accordto the necessary fineness in the following man- 7 ner:A highly heated gas stream of a temperature of 500-900 C. is led through a pipe in which 'the raw fuel, such as lumps of lignite, is discharged. By the sudden heating of the raw lignite in the quickly moving gas stream the exterior layer of the fuel is dried and bursts into small layers due to the great difference of the specific volumes of dry and wet fuel. The dried thereby coming again into the gas stream. This disintegrating (taking place simultaneously with the drying) may be supplemented by mechanical means,,e. g. a beater-drum by means of short, strong blows disintegrates the particles, which are too large, and which run back to the pipe. The dry and preferably dust fine coal is now separated by several dust removingdevices in series connected, namely first by a cyclone device gs and then by. an electric dust separator 7c. The gases discharged from 70 enter awasher l in order to be simultaneously cooled and freedfrom the last traces of dust; the liquids used in the washer may be e. g. water or a suspension of coal dust in water. The circulating gases are drawn out of Z and compressed by a fan or a blower m. One part of the cleansed gas is blown ofi at p. The rest is again forced into the device 11 wherethe re-heating of the circulating gas takes place.

oil by; a dust pump, for example by a Fuller pump r and forced through the dust conduit s into the gasifier at b. A certain portion of the whole of the dust produced is, however, drawn ofi at t through a separate conduit and passes to some separate point of consumption of coal dust.

The advantages of the present invention are the following:

(1). The present apparatus is considerably more simple than an' apparatus using normal circulating drying and normal dust gasification- :with circulating gas. Whereas, in' the normal construction the circulating drying and the dust of operation in which the heating of the circulating gas is effected by means of regenerators .(Figure 2). In this instance the dust gasificr (or gasiflers connected in series) is again denoted by 0., whereas the dust to be gasifled enters at b and the highly heated circulating gas at c. Gasifled fueldust and ceoledcirculating gas flows out at d, whereas the tcoal to be dried is introduced from the silo e through the device 1' into the circulating drier.- The dust separators g and k again eifect the purification of thecirculating gases.

In the washer Z the gas is finally cooled and washed, before the blower or the fan m brings the moving gas into circulation. A part of the gasification must each have a carefullyconstructbelow normal, the quantity of dust again sup' plied to the gasifier'increases automatically be-' cause the ungaslfied dust is returned to the gasiher in the continuous circuit,,so that, the circuproduced gas is againwithdrawn at p. The cold circulating gas enters the two regenerators 2i and as at 1:1 and an. Instead of two regenerators several regenerators may be used. The highly heated gases flow out of ,the regenerators alternately at 3/1 and 112 and again en'terthe gasifier at c.

latiori of s. somewhat' greater"quantity of dust In order, however, to prevent the ash content in the circulation from becoming too .great, a certain portion of the dust coal-isjalways drawn off and thus removed from the ci'rculation'together with the ash. This portion of the dust coal may be used for some other purpose. The quantities ofash and fuel dust removed frcm the circulation, however, need not beparticularly great in rder to keep the average ash content .ash must he introduced per 4 hour. amount of ash therefore amounts .to 3.2 tons per low, as the following example shows:-'

f to bepassed hourly through the dust gasifler.

However, enough coal must be. dried hourly to.

30 tons of dry coal dust containing 8% are obtain about 10 tons of coal dust 01 normal comcoal. Consequently 40 tons of coal dust with.8.% The total hour. Therefore 3.2 tons of ash must be removed with 9.2 tons of ash-free coal dust the latter being removed for some other purposes. Consequently,

. T takes the place of amore intensive gasification. 30v

For the re-heating of the regenerators highly heated air is introduced at w and as and hot as at-wrand wz the flue gases escaping at mV and v2 'duringthe heating period. The heating of thecombustion air to a high temperature is effected in anair heater-n. A fan i sucks in the air and forces it through the air heater into the regenerator which is actually to be heated. The air heater n is heated with a coal dust flame. The coal dust necessary for this heating is taken from the collecting silo in the following manner.

The coal dust passes from the dust separator through the conduits qr and 112 into a dust bunker 0. The. greater portion of the ash and fuel dust :5

*is pumped, by a dust pump or a'similar dev ce, for example by a Fuller pump, through a conduit s into the dust gaslfier at In. The dust pump it draws a certain. portion of the dust out of the cir-' culation and supplies'it to the furnace for heat-. ing the air heater.

If it should be found that; the ash content of the dust from the several dust separators is difposition, that is with 8% ash, which composition corresponds to about 9.2 tons of ash-free dust ferent, the quantity of dust, which is removed from circulation can preferably be drawn from the dust separator showing the highest ash content. In this manner the ash content in the dust f in circulation and in the dust introduced to the gasifier is further-reduced.

The most import'aht feature of the presentinventioniis in the combination of a special method .ior gasifying (i. 'e. gasifying of dusty fuels in.

itis'necessary to remove 12.4 tons of coal dust with an average ash content of 26%. 'With this ashcontent'it is possible'to directly employ the coal dust which is drawn out of the circulation.

provided it is for burning purposes; On the other hand the average ash content'in the coal arriving at the gasifier is just as high. However,

the gasification, can still be satisfactorily carried out with such an' ash content of the'coal. 7 It is therefore evident'thatby the manner of operation indicated,-, that is by the continual returning of the dust coming from the gasiflcation, combined with-a simultaneous withdrawing of a dust m xture from freshly dried dust and from dust returned from the gasification, it is possible to suspension by means of highly heated circulating gas) with a special '(circulating") method of' drying relatively wet, solid fuel. The circulating gases escaping from the gasifying zone and showing a temperature of about 500-300 C., are still charged with the ungasifled' part of the fuel dust. The lumps of raw material to be dried are introduced into this mixture of circulating gas 7 and of more or less gasifiedfuel; The fuel coming from the gasifying zone, and already partially.

gasifled is separated-together with the dusty fuel newly produced by the drying. A part of this .dustyfuel 'isre-introd'ucedinto the gasifying maintain at a satisfactory percentage the ash content of the fuel dust entering the gasifier.

This results in a considerable increase inthe efliciency, of the dust gasifie'r, as the latter is no.

longer 'dependent upon a high degree of gasiflca- -..tionjlecause, with a lower degree of gasification,

the quantity of dust increases. v

A special condition presents itself by the mode returning to the g'asifler zone," the other part being removed from circulation. If there were no removal of a certain,

quantity of fuel from the circulation, the ashcontent would be alwaysflncreased. No removal of ash from the gasifying'zone-as usualfin other processes-takes place, but a relatively small part of the fuel is removed, which is not or only partially gasified. Having thus described the invention, I claim: 1. The herein described process of gasifying carbon fuel, comprising the steps of heating the finely divided fuel in a gasifying zone by means of a gas stream of 700 to 1600? C. containing water vapor thereby bringing said water vapor in reaction with. said fuel, withdrawing from said gasifying zone a gas stream containing the finely divided fuel ash as well as any finely divided'unreacted fuel particles, introducing into said latter undivided gas stream, before it has finely divided fuel in a gasifying zone by means of a gas stream of 700 to 1600 C. containing water vapor thereby bringing said water vapor in reaction with said fuel, withdrawing from said gasifying zone a gas stream containing the finely divided fuel ash as well as any finely divided unreacted fuel particles, introducing into said latter undivided gas stream, before it has passed a separator, raw fuel to dry and disintegrate the same, separating at least part of the gas from said fuel dust and disintegrated fuel, returning at least part of said fuel dust and disintegrated fuel to said gasifying zone, charging part of said gas with a fresh quantity of the water vapor, reheating said part of the gas and returning it to the gasifying zone.

3. The herein'described process of gasifying carbon fuel, comprising the steps of heating the finely divided fuel in a gasifying zone by means of a gas stream of 700 to 1600 C. containing water vapor thereby bringing said water vapor in reaction with said fuel, withdrawing from said gasifying zone a gas stream containing the finely divided fuel ash as well as any finely divided unreacted fuel particles, introducing into said latter undivided gas stream, before it has passed a separator, raw fuel to dry and disintegrate the same, separating at least part of the gas from said fuel dust and disintegrated fuel, returning at least .part of said fuel dust and disintegrated fuel to said gasifying zone, washing the separated gas, whereby it becomes saturated 'with water, reheating part of said water-saturated gas, and returning said reheated gas to said gasifying zone.

4. The herein described process of gasifying carbon fuel, comprising the steps of heating the finely divided fuel ina gasifying zone by means of a gas stream of 700 ,to 1600 C. containing water vapor thereby bringing said. water vapor in reaction with said fuel, withdrawing from said gasifying zone a gas stream containing the finely divided fuel ash as well as any finely divided unreacted fuel particles, introducing into said latter undivided gas stream before it has passed a separator, raw fuel tofdry and disintegrate the same, separating at least part of the gas from said fuel dust and disintegrated fuel, returning 7 part of said fuel dust andidisintegrated fuel to said gasifying. zone, washing the separated gas whereby it becomes saturated with water, using the remaining part of said fuel dust and disintegrated fuel to reheat part of said water saturated gas, and returning said reheated gas to said gasifying zone.

HANS SCHZMAIETELDT. 

